Commercial production of viral vaccines typically require large quantities of virus as an antigen source. Commercial quantities of virus for vaccine production may be achieved by culture and replication of a seed virus in a cell culture system. Cell culture systems suitable for viral replication include mammalian, avian or insect cells, but mammalian cell culture systems are particularly preferred for viral vaccines to ensure proper glycosylation and folding of the virus' antigens proteins. For similar reasons, mammalian cell culture systems are also preferred for recombinant protein expression.
If unmodified from their naturally occurring states, cell cultures have a limited ability to reproduce, and subsequently are impractical and inefficient for producing the amount of material necessary for a commercial vaccine or recombinant protein. Consequently, for manufacturing purposes, it is preferred that the cells are modified to be “continuous” or “immortalized” cell lines to increase the number of times they can divide. Many of these modifications employ mechanisms similar to those which are implicated in oncogenic cells. As such, there is a concern that any residual materials from the cell culture process, such as host cell DNA, be removed from the final formulation of a vaccine or recombinant protein product manufactured in these systems.
A standard way of removing residual host cell DNA is by DNase treatment. A convenient method of this type is disclosed in European patent 0870508 and U.S. Pat. No. 5,948,410, involving a two-step treatment, first using a DNase (e.g. Benzonase) and then a cationic detergent (e.g. CTAB).
Current efforts to reduce this risk have focused on reducing the total concentration of residual host cell DNA. It is an object of the present invention to reduce the risk further by eliminating the functionality of any remaining host cell DNA.